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The indicated metal-centered radical arises from the laser-flash photolysis of the dinuclear complex [Rh(dmgH),PPh312. In the absence of other reagents the radical (which shows an absorption maximum at 580 nm, t = 2 X lo3 L mol-' cm-I) dimerizes rapidly, with kD = 2.3 X lo8 L mol-' s-' in 95% ethanol. The metal-centered radical reacts rapidly with 02, k = 1.4 X lo9 L mol-I s-l, with the first step assigned to the formation of a 1:l oxygen adduct. This reaction ultimately yields hydrogen peroxide. The reactions between Rh(dmgH),PPh, and a wide range of alkyl halides have also been studied. The rate constants kRx span a wide range, from -4 X lo2 (CHC1,) to 9 X lo8 (CBr.,). There is an approximate correlation between log kRx and the carbon-halogen bond dissociation energy. A correlation is also found with the half-wave potential for the reaction RX + e--R' + X-. The mechanism of the reactions with alkyl halides is discussed, and it seems probable that these reactions proceed by halogen atom abstraction.

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catalyzes the oxidation process, and it is notable that under analogous conditions oxidation has not been detected in V(V) systems.Several metal complexes of nicotinic acid A-oxide have been synthesized in aqueous and nonaqueous solvents.34,49 X-ray structure analysis has been done for some,49 showing that the ligand can coordinate in a monodentate manner via A-oxide oxygen or an oxygen of the carboxylato group. In addition, the ligand can be bidentate through both carboxylato oxygens or by bridging via a carboxylato oxygen and the A-oxide oxygen. Only an X-ray structure analysis could reveal the structure of molybdenum complexes 4-6. However, the spectral and chemical data (49) Knuuttila, H. Acta Chem. Scand., Ser. A 1983, A37, 697, 765. given have provided satisfactory evidence for the composition of the ligand sphere and the most likely mode of ligation to the molybdenum ion.The ligand spheres containing the combination of coordinated peroxo groups along with nicotinic acid or its A-oxide represent interesting example of peroxo-heteroligand V(V) and Mo(VI) complexes, where unusual electron transfers may be facilitated and where three biochemically relevant components are Combined in a compound. The structure, spectral properties, and reactivity of this type of compound are of interest and importance for biochemistry, as well as for many catalytical oxidations involving vanadium or molybdenum.Acknowledgment. Support of this work by the NSF (Grant No. CHE-8521376) is gratefully acknowledged.